Making Predator Control more Cost-Effective
Capturing natural prey odours as lures for stoats
Reference as:
Byrom, Andrea; Spurr, Eric & O'Connor, Cheryl, 2001: Making predator control more cost effective: capturing natual prey odours as lures for stoats. ConScience 42: pp.10-12.
Scent lures are used extensively overseas by commercial trappers of fur-bearing animals. Trappers in New Zealand report that ferret lures work as well as rabbit meat bait, and are better at attracting only ferrets than is rabbit meat.
Preliminary research by Landcare Research in pen trials using captive stoats has identified natural prey (rat and mouse) odours as highly attractive to captive stoats, compared to other odours tested. Rodent odours are much more attractive to stoats than egg odours, for example. Likewise, stoats are attracted to whole mice, whole rats, and chunks of rabbit and beef when these items are used as bait.
The problem with using dead natural prey (e.g. rodents) as lures or baits is that, although they are more attractive than eggs, they decay rapidly. The Department of Conservation has successfully used freeze-dried rats as lures for stoats in Te Urewera National Park. The rats last for approximately 6 weeks before decaying. A more effective and longer-lasting lure could be useful and cost-effective for both trapping and poison baiting of stoats. Ideally, this lure would incorporate odours of natural prey such as mice, rats or rabbits.The key to capturing natural prey odours, and encapsulating them into a long-life lure or bait, is to ensure that the 'main ingredients' are captured. Within the complex blend of odours emanating from vertebrates, specific compounds may act as attractants to predators. It is not clear whether these compounds act singly or in combination. At Landcare Research we are currently developing several lures impregnated with rodent (mouse or rat) odours that may be suitable for stoat control.
Capturing natural prey odours as lures for stoats
Predation by stoats is a major factor in the decline of some of New Zealand's indigenous wildlife. Cost-effective ongoing control of stoat populations is therefore crucial in maintaining viable populations of native birds such as kiwi, kaka, and yellowhead. Currently, the main method of stoat control for the protection of native wildlife is to use Fenn traps in tunnels baited with hen eggs.
Preliminary research by Landcare Research in pen trials using captive stoats has identified natural prey (rat and mouse) odours as highly attractive to captive stoats, compared to other odours tested. Rodent odours are much more attractive to stoats than egg odours, for example. Likewise, stoats are attracted to whole mice, whole rats, and chunks of rabbit and beef when these items are used as bait.
The problem with using dead natural prey (e.g. rodents) as lures or baits is that, although they are more attractive than eggs, they decay rapidly. The Department of Conservation has successfully used freeze-dried rats as lures for stoats in Te Urewera National Park. The rats last for approximately 6 weeks before decaying. A more effective and longer-lasting lure could be useful and cost-effective for both trapping and poison baiting of stoats. Ideally, this lure would incorporate odours of natural prey such as mice, rats or rabbits.
The key to capturing natural prey odours, and encapsulating them into a long-life lure or bait, is to ensure that the 'main ingredients' are captured. Within the complex blend of odours emanating from vertebrates, specific compounds may act as attractants to predators. It is not clear whether these compounds act singly or in combination. At Landcare Research we are currently developing several lures impregnated with rodent (mouse or rat) odours that may be suitable for stoat control.
Why a 'long-life' lure or bait?
If an attractive long-life lure were available, it would make control of predators such as stoats more cost-effective for a number of reasons. Recent legislation (the Animal Welfare Act 1999) allowing managers to leave kill traps without checking them daily means that they may make significant savings in labour costs because field workers don't have to do the 'daily round'. These labour savings would be offset, however, if the lure in the kill trap declined in attractiveness over time. It is therefore crucial that the lure in the kill trap remains attractive to stoats while it is left out in the field. In addition, there may soon be at least two 'multiple capture' traps available on the market. Again, for these types of traps to be effective, they must continue to attract predators for several weeks or months at a time without being serviced.
Our study
Our research aims to develop methods for capturing the odours of the natural prey of stoats, and incorporating them into a long-life, slow-release matrix suitable for use under a variety of field conditions. In research funded by the Foundation for Research, Science and Technology, we previously determined the feasibility of developing odour-impregnated matrices by reviewing international literature and contacting workers in New Zealand and overseas to determine what has already been done encapsulating odours.
We found that methods for capturing prey odours can be classified into three main categories:
(1) Capturing volatile odour chemicals from live or dead prey onto absorbent material, and extracting and identifying those volatiles;
(2) Freeze-drying or grinding up fresh dead prey and incorporating the resulting compound into a suitable matrix; or
(3) Extracting the active ingredients from dead prey by immersing them directly into a solvent. Methods for developing a long-life, slow-release matrix, and encapsulating the extracted odours into that matrix, are equally diverse.
Possible candidates include a PVC matrix, a casein-based matrix known as Albert?manufactured by KiwiTech, a gel matrix manufactured by KiwiCare, or a pelletised meat and bone meal 'pill'. Each of these techniques has advantages and disadvantages, and finding the right combination of odour extraction and encapsulation into a suitable matrix poses quite a challenge. One thing is certain: methods that incorporate the entire suite of odours emanating from rodents (and not just one or two specific compounds) are most likely to succeed in attracting predators such as stoats.
In the past 10 months we have explored options for incorporating two 'rodent extracts' into suitable matrices. We now have several matrices suitable for testing for attractiveness to stoats.
The next steps
In the upcoming year we plan to determine the attractiveness of encapsulated rodent odours to 20 captive stoats at our animal facility at Lincoln. We plan to record the stoats' responses to odour-impregnated matrices on time-lapse video.
At this stage, we are using rodents (primarily lab rats, because they are readily available) as 'proof of concept', to determine whether techniques for odour extraction and encapsulation into suitable matrices are feasible (and commercially viable). Once a technique has been perfected, it will be possible to use ship rats or Norway rats when developing long-life lures. If rodents were obtained from the wild, this would also have the additional bonus of reducing their densities. The technique may also be suitable for use with other predator and prey species, e.g. ferrets and rabbits. In reality, a cost-effective long-life matrix that incorporates the odours of natural prey is at least 18 months away - but watch this space.
This research is funded by the Department of Conservation and is dealt with more fully in:
Byrom, A. E. and E. B. Spurr. 2000: Capturing odours of natural prey as lures for stoat control. Landcare Research Contract Report LC9900/131.
Thanks also to the Department of Conservation for permission to use this article.
If you would like to know more about ferret research in New Zealand or if you are interested in becoming involved in ferret research in your area, please contact:
Back
to top
 | Andrea Byrom Email  |
Landcare Research | |
Phone: +64 3 321 9999 |